[SI-LIST] Re: Simulating frequency dependent s-parameters in HSPICE
- From: Ray Anderson <ray.anderson@xxxxxxxxxx>
- To: Krishna Chaitanya <krishna1abc@xxxxxxxxx>
- Date: Mon, 12 Mar 2012 15:54:15 -0700
Krishna-
Yes, the s-parameters generated by Q3D take into effect the frequency
dependent parasitics (if you really must think of it that way) of the
interconnect.
Regarding how to select the sweep range, here are a few rules of thumb:
Extract the s-parameters over a range of DC to the highest frequency you
are interested in. You need to either get a DC point or at least as low
as possible such that the simulator can extrapolate down to DC. This is
necessary for Hspice to achieve convergence in most cases when it is
doing the time domain simulation.
As far as the sampling or step size, it all depends on "how interesting"
the response of your interconnect is. It it looks like a well behave
transmission line without a lot of resonances or other unexpected
perturbations then relatively coarse sampling might be OK (say 50 or 100
MHz). However if there are a lot of variations in the transfer function
due to resonance, reflections or whatever you may need to go to much
finer frequency steps to assure that you capture all the necessary
detail in your s-parameters. If you utilize adaptive sweep in your
extractor (I don't remember if Q3D implements that mode, HFSS does) then
the tool can usually determine the density of sampling to generate good
output data. Using regular linear or log sweep with too coarse of steps
can cause the extractor to jump over resonances and such and not even
notice they are there.
-Ray
Raymond Anderson
Senior Signal Integrity Staff Engineer
Programmable Platforms Development
Silicon Technology Group
Signal Integrity and Package Development Department
Xilinx Inc.
2100 Logic Drive
San Jose, California 95124
(408) 626-6277
From: Krishna Chaitanya [mailto:krishna1abc@xxxxxxxxx]
Sent: Monday, March 12, 2012 3:41 PM
To: Ray Anderson
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Simulating frequency dependent s-parameters
in HSPICE
Ray, Thank you very much for explaining it.
Can I say that when I provide s-parameters for HSPICE simulation, the
results do take into account the frequency dependent parasitics (RLGC as
s-parameters)?
I use Q3D extractor for s-parameter extraction. In Q3D extractor if I
provide a sampling frequency of 1GHz and range from 1G to 30G with step
size of 1G, does it mean the frequency effects till 30G are being
considered in my simulations?
On what factors should I determine my sampling frequency, frequency
range and step size for extracting s-parameters?
Thanks,
Krishna
On Mon, Mar 12, 2012 at 3:20 PM, Ray Anderson <ray.anderson@xxxxxxxxxx>
wrote:
Krishna-
The s-parameters you are using in your simulation ARE frequency
dependent.
The following is a small sample from a random Touchstone format
s-parameter file. Each line contains the scattering parameters ( in this
case, for a 2-port in Real/Imaginary format) for a specific sampled
frequency:
# KHz S RI R 50.00
3.00E+01 4.19E-01 -4.67E-01 5.81E-01 4.68E-01 5.81E-01 4.68E-01
4.19E-01 -4.67E-01
3.19E+01 3.91E-01 -4.62E-01 6.09E-01 4.62E-01 6.09E-01 4.62E-01
3.91E-01 -4.62E-01
3.39E+01 3.63E-01 -4.55E-01 6.37E-01 4.55E-01 6.37E-01 4.55E-01
3.63E-01 -4.55E-01
3.60E+01 3.37E-01 -4.47E-01 6.63E-01 4.47E-01 6.63E-01 4.47E-01
3.37E-01 -4.47E-01
The s-parameters could be converted to a lumped RLGC representation, but
for simulation in Hspice using the S-element that is NOT required (or
desired). Note that each line describes the 2-port s-parameters (S11,
S12, S21, S22 at a specific frequency). If necessary, the simulator can
interpolate between the frequencies in the Touchstone file.
When Hspice executes a time domain simulation as you have described it
will perform a convolution of the driving signal with the s-parameters
(in very simplistic terms) to arrive at the solution. It does not need
to determine RLGC values at a specific datarate.
-Ray Anderson
Xilinx Inc.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Krishna Chaitanya
Sent: Monday, March 12, 2012 2:42 PM
To: Ihsan Erdin; Sinha, Snehamay
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Simulating frequency dependent s-parameters in
HSPICE
Hi Snehamay, Ihsan and others,
Thank you very much for the SPICE syntax. I used that for the
simulations
but not clear how it guarantee frequency dependent RLGC are taken into
account.
When I give a PRBS input corresponding to a bit rate of say 2GBPS (or 1
GHz
of clk), does it mean the HSPICE will pick the RLGC values corresponding
to
this particular frequency of 1GHz?
I do not see any visible connection which tells the SPICE to pick the
RLGC
values corresponding to the input data rate.
Can you please help me understand what is happening when I simulate
using
s-parameters in HSPICE
On Mon, Mar 12, 2012 at 9:55 AM, Krishna Chaitanya
<krishna1abc@xxxxxxxxx>wrote:
> Thanks all. I have few questions.
>
> I did try using s-element and I am not clear how to interpret my
> simulation results.
> For a simple case of inverter based driver and receiver,
>
> INV (driver) -> Through Silicon Via (Interconnect) -> Inv (Receiver)
>
> I have the s-parameter touchstone file for a range of frequencies for
TSV
> extracted using Q3D extractor. I simulated this in HSPICE using
s-element
> and I got some eye diagram for a PRBS pattern for a particular input
data
> rate.
>
> From my understanding, the R and L values atleast change with
frequency
> and depending on that my eye opening should change.
> If I use the s-element method, I get a single eye diagram. How should
I
> interpret it?
> Does it mean the eye diagram which I get after simulating using
s-element
> includes the effect of all the frequencies on RLGC parasitics?
>
> In short I am not clear how s-element simulations guarantee that my
> simulation results include frequency dependent RLGC parasitics.
>
> Thanks,
> krishna
>
>
> On Mon, Mar 12, 2012 at 9:29 AM, Ihsan Erdin <erdinih@xxxxxxxxx>
wrote:
>
>> Krishna,
>>
>> In hspice, you can directly plug in those s-parameters to your
netlist as
>> an s-element. As there's no need for a w-element using one wouldn't
be
>> right either. You can model the rest of the tracks with the
w-element.
>> Below, I suspect you're referring to a totally different case which
is
>> about assigning freq. dependent PUL parameters to the w-element from
a
>> touchstone file. This can only be be used when the track parameters
are
>> computed with a third party tool and completely irrelevant to what
you're
>> trying to accomplish in this particular situation -if I understood
your
>> case correctly, of course...
>>
>> Regards,
>>
>> Ihsan
>>
>> On Mon, Mar 12, 2012 at 11:28 AM, Krishna Chaitanya <
>> krishna1abc@xxxxxxxxx> wrote:
>>
>>> Hello All,
>>> I am trying to analyze the impact of frequency dependent parasitics
of
>>> Through Silicon Vias on data rate. I used Ansoft Q3D extract to
obtain
>>> RLGC
>>> parasitics as s-parameter Touchstone file for a range of
frequencies.
>>> Now I
>>> would like to know how can I use this file in HSPICE simulation.
When I
>>> use
>>> w-element method in HSPICE it can take touchstone file as input but
I am
>>> not sure whether it is the correct way to simulate any frequency
>>> dependent
>>> parasitics in HSPICE.
>>>
>>> Any help?
>>>
>>> Thanks,
>>> Krishna
>>>
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